This invention relates generally to proteinaceous materials containing single-cell proteins, and more specifically, to a texturization process for mixtures of single-cell proteins combined with plant and/or animal proteins which includes mixing, moisturizing, heat-extruding, chopping, drying and cooling to induce texture formation.
In recent years much attention has been directed toward the development of new sources of protein which can be incorporated in foods or food additives suitable for human consumption. Rapid increases in world population have made the continued dependence on traditional sources of protein highly impractical. Moreover, the supply of protein from typical sources of protein, such as animal meat and certain vegetables, is inadequate to provide balanced diets sufficient to satisfy the needs of humans throughout the world.
One possible solution to the problem of supplying the ever-increasing need for food protein is provided by processes for the bio-synthetic manufacture of protein through the growth of microorganisms on hydrocarbons or other substrates. It is known, for example, that microorganisms such as bacteria, fungi, and yeast, which are grown by single-cell reproduction, contain high proportions of proteins and can be utilized directly in foods as a whole cell material or can be treated to recover protein concentrate and protein isolate. Recent efforts have shown that microorganisms, grown on hydrocarbon substrates, can be successfully used in animal feeds; but as yet these microorganisms have not been commercially accepted in food preparations suitable for human consumption.
With the development of successful processes for the fermentation production of protein-containing microorganisms (sometimes referred to herein as single cell proteins), an urgent need has developed for methods of texturizing such single-cell protein materials in a manner sufficient to render them suitable alone or in combination with plant and/or animal proteins for use in food products.
Generally, single-cell protein is initially produced as a slurry and then is subsequently converted into dry powder form. This dry powder, similar in appearance and feel to flour, lacks the texture and food-like sensation to the mouth necessary to make an attractive food. Moreover, when placed in water, the agglomerated particles of single-cell protein rapidly revert back to single-cell form.
As a result of worldwide meat shortages and increased cost and low production efficiency of cattle, fowl and fish, the interest in and production of meat, poultry and fish analogs by using vegetable (plant) protein materials have increased during the recent years. Currently, the most successful process from a texture and flavor point of view is the spinning process for the isolated protein (particularly isolated soy proteins). The spun protein meat analogs have uniform "rod-like" fibrous texture, but when chewed the fibers disperse like "cotton" in the mouth rather than exhibiting a "biting" texture typical of meat. The textured soy flour or soy concentrate products, obtained by extrusion or other processes, do not have any desirable meat appearance or bite. Furthermore, they have a beany taste and aftertaste. We discovered that incorporation of yeast into the soy flour and soy concentrate helps create a meatlike appearance without the need for spinning. The yeast-containing product has also a meatlike chewability. Although yeast partially masks the soybean taste, a sweet-toasted taste exists in all products that are based on soy flour, soy concentrate and yeast mixtures. Such flavors may interfere with the delicate meat, poultry, and fish flavors expected from the meat analogs. We have discovered that such non-meatlike flavors can be removed by washing with water, acidified water or alkaline water at various temperatures. The washed products had improved meatlike textures and they could be flavored to resemble meat, poultry and fish tastes. As we were studying the extrusion texturization of our protein mixtures, we observed that the extrudate retains its thermoplastic properties for a short period immediately after it leaves the die and it can be further shaped. We were surprised to see that the extrudate expanded like rubber when pulled immediately after it left the die. Moreover, as the extrudate lost its thermoplastic character by cooling during pulling, the fibrous meatlike texture was improved and it had the textured mouth feel of meat when hydrated and chewed. The same textured character develops if the extrudate after it leaves the die, or the "set" dry extrudate, is wetted with water and then a friction force is applied such as rolling between fingers.
The living world is divided into three "kingdoms"--plant, animal and protist. The first two are multicellular and their development always involves extensive tissue differentiation. Protists are generally unicellular and lack tissue differentiation. Typical protists include yeasts, fungi and bacteria. Stated differently, protists represent the simplest level of biological organization while even the lower plants and animals represent vastly more complex biological organizations.
Unicellular protists such as yeasts, fungi and bacteria are extremely minute and contain desirable protein enclosed within a cell-wall structure comprising essentially carbohydrate materials. The amino acids comprising the protein of unicellular protists are substantially those involved in the larger protein-containing aggregates of plant or animal origin.
The cell-wall structure may be viewed as a tough, large, bag fashioned from highly cross-linked polysaccharides. Consequently the protein moiety of each cell is shielded from that of every other cell. Hence, the intermolecular bonding forces which are thought to readily effect texturization of protein found within multi-cellular plant or animal structures cannot be utilized unless some means be found for freeing some portion of protein from within the cell structure. This distinctive structure of unicellular protists has heretofore severely limited the utility of yeasts, fungi and bacteria in food products because of inability to effect a suitable and stable degree of texturization.